Waveguide bandpass filters are known in the art and are commonly used in microwave equipment for communications and military applications. Waveguide bandpass filters help to eliminate undesired radiation and unwanted frequencies that can cause interference, by rejecting and/or reducing these unwanted frequencies from a desired frequency passband that is allowed to travel through the waveguide bandpass filter.
Waveguide bandpass filters are generally constructed out of rectangular tubes into which two or more resonant cavities are formed. The resonant cavities are coupled together such that electromagnetic waves within a desired frequency passband can be transmitted through the waveguide bandpass filter. Shown in FIG. 1 is a cross-sectional diagram of an existing type of direct-coupled bandpass filter 4 that is known in the prior art. Included within the filter 4 are resonant cavities 6 that are positioned between two adjacent coupling elements 8. The coupling elements 8 are formed by irises. However, other coupling structures are also known in the art, such as posts, dents or holes. Once constructed, in order to obtain precision coupling, tuning of the couplings often needs to be performed. It is thus known to provide coupling screws that extend beside/between the walls of the irises, in order to be able to trim the coupling and obtain the precision coupling that is desired between two resonant cavities. Tuning screws are then positioned within the resonant cavities 6, between two coupling elements 8, for trimming the resonant frequencies of the resonant cavities 6.
In general, waveguide bandpass filters are quite costly to manufacture, as they can require complex machining and soldering operations in order to get the exact shapes and configurations necessary to achieve the coupling and tuning of the resonant cavities. Accordingly, there is a need in the industry for an improved waveguide bandpass filter that is less costly and less complicated to manufacture, such that it alleviates, at least in part, the deficiencies of existing waveguide passband filters.